Sealing material sheet for solar-cell module and solar-cell module using the same

ABSTRACT

To provide a sealing material sheet for a solar-cell module that has high productivity without performing crosslinking processing, and has a high tensile shear adhesion force at normal temperature at a high level in addition to heat resistance and molding characteristics. A sealing material sheet is a multi-layer sheet using a polyethylene-based resin as a base resin, a core layer 11 has a density of 0.880 g/cm3 to 0.930 g/cm3 and a melting point of 70° C. or higher, a skin layer 12 has a density of 0.880 g/cm3 to 0.900 g/cm3 and a melting point of 90° C. or lower and contains a silane-modified polyethylene-based resin, a weight average molecular weight of the silane-modified polyethylene-based resin contained in the skin layer 12 in terms of polystyrene is 70000 to 120000, and a polymerized silane amount of the skin layer 12 in the whole resin component is 300 ppm to 2000 ppm.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a sealing material sheet for asolar-cell module and a solar-cell module using the same. Specifically,the present invention relates particularly to a sealing material sheetthat can be preferably used in a double-sided glass protecting substratetype solar-cell module and a double-sided glass protecting substratetype solar-cell module using the same.

Related Art

Recently, as awareness of the environmental problems rises to a higherlevel, solar cells are in the spotlight as clean energy sources.Currently, solar-cell modules that are constituted in various types aredeveloped and suggested. There are various layer constitutions insolar-cell modules, but as a constitution that is particularly excellentin barrier property for preventing intrusion of moisture into a module,long-term durability in harsh use conditions, and the like, a solar-cellmodule having a constitution in which both a front-surface protectingsubstrate and a rear-surface protecting substrate are configured by aprotecting substrate made of glass is also devised (see Patent Document1). Incidentally, in the present specification, the solar-cell modulehaving a constitution in which protecting substrates disposed on bothoutermost surfaces of a module main body are configured by a glasssubstrate in this way is referred to as a “double-sided glass protectingsubstrate type solar-cell module.”

Conventionally, as a sealing material sheet used in a solar-cell module,also including a double-sided glass protecting substrate type solar-cellmodule, from the viewpoints of processability, workability,manufacturing cost, and the like, an ethylene-vinyl acetate copolymerresin (EVA) has been mainly used. However, the EVA resin tends to slowlydecompose as it is used for a long period of time, and thus, there is apossibility of generating acetic acid gas affecting a solar cellelement. For these reasons, in recent years, a demand for a sealingmaterial sheet for a solar-cell module using a polyethylene-based resininstead of the EVA resin has been increasing (see Patent Document 2).

In general, transparency and flexibility of the sealing material sheetfor a solar-cell module using a polyethylene-based resin as a base resincan be improved by decreasing the density thereof. However, on the otherhand, a decrease in density causes problems such as insufficient heatresistance. In this regard, in the sealing material sheet of PatentDocument 2, the heat resistance is imparted by a crosslinking agent. Inthis case, the heat resistance is reliably improved. However, when acrosslinking treatment is performed to an extent that is sufficient andnecessary for providing sufficient heat resistance to be endurable for along-time use under a high temperature, a problem arises in thatfollowability (hereinafter, referred to as “molding characteristics”) toirregularities on a surface of a facing member cannot be maintained, atthe time of modularization. Further, in manufacturing processingnecessarily including a crosslinking treatment, film formation abilitydecreases as the crosslinking progresses during molding. Therefore, itis required to carry out molding at a low temperature and to carry outcrosslinking reaction again after molding, and it is required to furtherimprove productivity.

For example, as a sealing material sheet that is intended to achieveboth heat resistance and molding characteristics without undergoing acrosslinking treatment, there is disclosed a sealing material sheet thatis intended to achieve both heat resistance and molding characteristicswithout performing the crosslinking treatment by being configured as amulti-layer sheet obtained by combining a skin layer, which is obtainedby mixing two or more kinds of resins each having a different meltingpoint, and a core layer formed from a sealing material composition addedwith a nucleating agent such as inorganic particles (see Patent Document3).

Patent Document 1: Japanese Unexamined Patent Application, PublicationNo. 2013-9258164

Patent Document 2: Japanese Unexamined Patent Application, PublicationNo. 2009-10277

Patent Document 3: PCT International Publication No. WO2012/073971

SUMMARY OF THE INVENTION

The double-sided glass protecting substrate type solar-cell module thathas been widely used in recent years has a frameless structure in whicha metallic frame surrounding a module side surface is excluded, in manycases (see Patent Document 1). In this case, in addition to achieving ofboth the heat resistance and the molding characteristics mentionedabove, a high tensile shear adhesion force (an adhesion force accordingto JIS K 6850 Adhesives-Determination of tensile lap-shear strength ofrigid-to-rigid bonded assemblies) at normal temperature is required inthe sealing material sheet in terms of the structure of the solar-cellmodule. There is no sealing material sheet, which meets threerequirements of the heat resistance, the molding characteristics, andfurther a high tensile shear adhesion force at normal temperature at ahigh level, yet.

The present invention was made in view of the above circumstances. Anobject of the present invention is to provide a sealing material sheetfor a solar-cell module that is a sealing material sheet using apolyethylene-based resin, has high productivity without performingcrosslinking processing, and has a high tensile shear adhesion force atnormal temperature at a high level in addition to heat resistance andmolding characteristics.

The inventors of the present invention conducted a thoroughinvestigation, and as a result, the inventors found that theabove-described problems can be solved by a sealing material sheet beingconfigured as a multi-layer sheet having a constitution of a skinlayer-a core layer-a skin layer, a predetermined amount range of asilane-modified polyethylene-based resin being contained in the skinlayer while a melting point of the core layer is maintained to 70° C. orhigher, and this silane-modified polyethylene-based resin beingspecified to be in a specific high molecular weight range. Thus, theinventors finally completed the present invention. More specifically,the present invention provides the following.

(1) A sealing material sheet for a solar-cell module, the sealingmaterial sheet being a multi-layer sheet using a polyethylene-basedresin as a base resin and including a core layer and a skin layerdisposed on both outermost surfaces, in which the core layer has adensity of 0.880 g/cm³ to 0.930 g/cm³ and a melting point of 70° C. orhigher, the skin layer has a density of 0.880 g/cm³ to 0.900 g/cm³ and amelting point of 90° C. or lower, and the skin layer contains asilane-modified polyethylene-based resin, a weight average molecularweight of the silane-modified polyethylene-based resin contained in theskin layer in terms of polystyrene being 70000 to 120000, a polymerizedsilane amount of the skin layer in the whole resin component being 300ppm to 2000 ppm.

(2) The sealing material sheet described in the above (1), in which theweight average molecular weight of the silane-modifiedpolyethylene-based resin contained in the skin layer in terms ofpolystyrene is 90000 to 120000.

(3) The sealing material sheet described in the above (1) or (2), inwhich melting points of the core layer and the skin layer are both 70°C. to 80° C.

(4) A solar-cell module obtained by sequentially laminating atransparent front substrate, a sealing material of a light receivingsurface side, a solar cell element, a sealing material of a non-lightreceiving surface side, and a rear-surface protecting substrate, thesealing material of the light receiving surface side and the sealingmaterial of the non-light receiving surface side being the sealingmaterial sheet according to any one of the above (1) to (3).

(5) The solar-cell module described in the above (4), in which both thetransparent front substrate and the rear-surface protecting substrateare a protecting substrate made of glass.

(6) The solar-cell module described in the above (5), in which thesolar-cell module is a frameless module having no protecting frame thatsurrounds a circumference of a side surface of a module laminateinterposed between the protecting substrates made of glass to maintain ashape of the module laminate.

(7) The solar-cell module described in any one of the above (4) to (6),in which, in a surface of the solar cell element, convex portions formedby a part of the surface protruding in a line-shaped manner or adot-shaped manner exist, the convex portions being buried inside thesealing material sheet laminated on the surface, and a thickness of theconvex portion is 50% to 90% of a thickness of the sealing materialsheet laminated on the surface of the solar cell element.

According to the present invention, it is possible to provide a sealingmaterial sheet for a solar-cell module that is a sealing material sheetusing a polyethylene-based resin, has high productivity withoutperforming crosslinking processing, and has a high tensile shearadhesion force at normal temperature at a high level in addition to heatresistance and molding characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view schematically illustrating a layerconstitution of a sealing material sheet of the present invention.

FIG. 2 is a cross-sectional view illustrating an example of a layerconstitution of a double-sided glass protecting substrate typesolar-cell module that is formed using the sealing material sheet of thepresent invention.

FIG. 3 is a sectional view schematically illustrating an example of alayer constitution of a solar-cell module that is formed using thesealing material sheet of the present invention and a thin film solarcell element.

FIG. 4 is a partially enlarged view of FIG. 3 and is a view fordescription of molding characteristics of the sealing material sheet ofthe present invention in the case of being used in a thin filmsolar-cell module.

FIG. 5 is a partially enlarged cross-sectional view of a conventionalsolar-cell module using a conventional sealing material sheet inferiorin molding characteristics as a thin film solar-cell module.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, a sealing material composition that can be used inmanufacturing of a sealing material sheet for a solar-cell module of thepresent invention, a sealing material sheet for a solar-cell module ofthe present invention, and a solar-cell module using the sealingmaterial sheet of the present invention will be sequentially described.

<Sealing Material Composition>

The sealing material sheet of the present invention can be manufacturedby melt molding a sealing material composition that will be hereinafterdescribed in detail. The sealing material composition is separated foreach layer into a sealing material composition for a core layer and asealing material composition for a skin layer. Further, when amulti-layer sheet having a three-layer constitution that includes a corelayer as an inner layer and a skin layer as an outermost surface layeris formed by those respective sealing material compositions for a corelayer and a skin layer, the sealing material sheet of the presentinvention typified, for example, by the sealing material sheet 1illustrated in FIG. 1 can be manufactured. Incidentally, in the presentspecification, the skin layer refers to a layer that is disposed at bothoutermost surface sides of the multi-layer sealing material sheet.Further, the core layer refers to an inner layer other than the skinlayer in the multi-layer sealing material sheet. In the sealing materialsheet of the present invention, the core layer itself may further have amulti-layer inner constitution, but the sealing material sheet 1 havinga three-layer constitution in which a skin layer is laminated on bothsurfaces of the core layer having a single layer constitution is atypical embodiment of the present invention. Hereinafter, an embodimentof the present invention will be described with a focus on this sealingmaterial sheet 1.

[Sealing Material Composition for Core Layer]

The sealing material composition for a core layer is a thermoplasticsealing material composition that uses a polyethylene-based resin as abase resin, does not contain a crosslinking agent, and does not needcrosslinking processing at the time of molding a sealing material sheet.Further, the sealing material composition for a core layer may containan appropriate amount of other resins such as a silane-modifiedpolyethylene-based resin and other components, other than a low-densitypolyethylene-based resin (LDPE) or the like as a base resin, in a rangethat does not impair the effect of the present invention.

As the base resin of the sealing material composition for a core layer,a low-density polyethylene-based resin (LDPE), a linear low-densitypolyethylene-based resin (LLDPE), or a metallocene-based linearlow-density polyethylene-based resin (M-LLDPE) can be preferably used.Of them, from the viewpoint of long-term reliability of the solar-cellmodule, a low-density polyethylene-based resin (LDPE) can beparticularly preferably used as the sealing material composition for acore layer. Incidentally, the “base resin” in the present specificationrefers to a resin having the largest content ratio in the resincomponent of the resin composition, in the resin composition containingthe base resin.

It is preferable that the sealing material composition for a core layerfurther contains a predetermined amount of a silane-modifiedpolyethylene-based resin in addition to the above-described base resin.In the sealing material composition for a core layer, thesilane-modified polyethylene-based resin is not necessarily an essentialcomponent, but in a case where a silane-modified polyethylene-basedresin is contained in the sealing material composition for a core layer,it is preferable that the silane-modified polyethylene-based resin is asilane-modified polyethylene-based resin having a weight averagemolecular weight in terms of polystyrene of 70000 or more (hereinafter,this is also referred to as a “high molecular weight typesilane-modified polyethylene-based resin”).

Regarding the amount of the high molecular weight type silane-modifiedresin added to the sealing material composition for a core layer, it ispreferable that the high molecular weight type silane-modified resin iscontained in the sealing material composition for a core layer at such aproportion that the polymerized silane amount of a core layer 11 in thewhole resin component becomes 30 ppm to 2000 ppm. When an appropriateamount of such a high molecular weight type silane-modifiedpolyethylene-based resin is contained in the sealing materialcomposition for a core layer, this can contribute to improvement in hightensile shear adhesion force of the sealing material sheet 1 at normaltemperature. Incidentally, regarding the polymerized silane amount ineach layer of the sealing material, the abundance in the resin componentcan be specified, for example, by quantitating elements in each layer byICP emission analysis or the like. Details of the high molecular typesilane-modified resin that can be used in the sealing material sheet 1will be described later.

The density of the sealing material composition for a core layer is0.880 g/cm³ to 0.930 g/cm³, preferably 0.880 g/cm³ to 0.920 g/cm³, andmore preferably 0.885 g/cm³ to 0.895 g/cm³. When the density of thesealing material composition for a core layer is set in theabove-described range, the heat resistance and the moldingcharacteristics can be provided to the sealing material sheet 1 at agood balance without undergoing the crosslinking treatment.

The melting point of the sealing material composition for a core layermay be 70° C. to 110° C. and is preferably 73° C. to 90° C. As long asthe melting point of the core layer 11 of the sealing material sheet 1can be maintained in the above-described range, polyethylene-basedresins each having a different melting point can be appropriately mixedto obtain a sealing material composition for a core layer. For example,according to a resin composition obtained by mixing three kinds ofpolyethylene-based resins respectively having melting points of 60° C.,90° C., and 97° C. in each amount of 65 parts by mass, 8 parts by mass,and 32 parts by mass, the melting point of the whole core layer can beset to 74° C., and a blending example of such material resins can beexemplified as a preferable resin blending example of the sealingmaterial composition for a core layer.

Herein, the melting point in the present specification refers to anaverage of each intrinsic melting point of each component contained in ameasurement target product and melting points obtained by calculationfrom the blending ratio of these components.

For example, the melting point of the sealing material sheet or eachresin layer constituting the sealing material sheet according to theabove-described definition can be measured by differential scanningcalorimetry (DSC). In a case where there are a plurality of peaks of avalley in the DSC curve, the melting point shown by a peak having thelargest peak area among the peaks can be regarded as the melting pointof the sealing material sheet or each resin layer described above.

Further, as another method of specifying the melting point from thesealing material sheet according to the above-described definition,there is mentioned a method of measuring a linear expansion peaktemperature that is a temperature in the largest value at which a linearexpansion coefficient shifts from increase to decrease in a case where ameasurement linear expansion coefficient measured according to JIS K7179 is represented as a function of a resin temperature. According tothis method, the melting point according to the above-describeddefinition can be approximately specified from a completed product suchas a sealing material sheet in a variation range within roughly about 2°C.

When the melting point of the sealing material composition for a corelayer is maintained to 70° C. or higher as described above, heatresistance necessary for the sealing material sheet 1 can be imparted.Further, in a relation with heating conditions at the time of meltmolding for forming a sheet as the sealing material sheet and at thetime of a thermal lamination treatment for integration as the solar-cellmodule, the melting point of the sealing material composition for a corelayer may be generally about 110° C. or lower, and in order tosufficiently enhance the molding characteristics of the sealing materialsheet 1, the melting point of the sealing material composition for acore layer is more preferably 90° C. or lower.

The melt mass flow rate (MFR) of the sealing material composition for acore layer may be 3.0 g/10 min or more and less than 5.0 g/10 min, andas long as the MFR is in this range, a polyethylene-based resin havingan MFR of 0.8 g/10 min or more and less than 5.0 g/10 min can beappropriately mixed and used. When the MFR of the sealing materialcomposition for a core layer is set in the above-described range, theheat resistance and the molding characteristics can be provided to thesealing material sheet 1 at a good balance.

Incidentally, the MFR in the present specification is a value obtainedby the following method unless otherwise particularly specified. MFR(g/10 min): measured according to JIS K 7210. Specifically, a syntheticresin was heated and pressurized at 190° C. in a cylindrical vesselheated by a heater, and the amount of the resin extruded per 10 minutesfrom an opening (nozzle) provided at the bottom of the vessel wasmeasured. An extrusion plastometer was used as a testing machine and theextrusion load was 2.16 kg. Incidentally, regarding the MFR of themulti-layer sealing material sheet, a measurement value obtained byperforming the measurement by the above-described treatment while thewhole layers are in a multi-layer state of being integrally laminated isused as the MFR value of the multi-layer sealing material sheet.

[Sealing Material Composition for Skin Layer]

The sealing material composition for a skin layer is also athermoplastic sealing material composition that uses apolyethylene-based resin as a base resin and does not contain acrosslinking agent, similarly to the sealing material composition for acore layer. Further, the point that an appropriate amount of othercomponents may be contained in a range that does not impair the effectof the present invention is the same as in the sealing materialcomposition for a core layer. However, the sealing material compositionfor a skin layer is different from the sealing material composition fora core layer in that it is essential to contain a specific amount of asilane-modified polyethylene-based resin having a weight averagemolecular weight in terms of polystyrene of 70000 or more (highmolecular weight type silane-modified polyethylene-based resin).

As the base resin of the sealing material composition for a skin layer,similarly to the sealing material composition for a core layer, alow-density polyethylene-based resin (LDPE), a linear low-densitypolyethylene-based resin (LLDPE), or a metallocene-based linearlow-density polyethylene-based resin (M-LLDPE) can be preferably used.Of them, from the viewpoint of molding characteristics, ametallocene-based linear low-density polyethylene-based resin (M-LLDPE)can be particularly preferably used as a composition for the skin layer.

The sealing material composition for a skin layer used in the sealingmaterial sheet 1 further contains a predetermined amount of asilane-modified polyethylene-based resin as an essential resin componentin addition to the above-described base resin. Further, thesilane-modified polyethylene-based resin contained in the compositionfor the skin layer is limited to a silane-modified polyethylene-basedresin having a weight average molecular weight in terms of polystyreneof 70000 or more (hereinafter, also referred to as “high molecularweight type silane-modified polyethylene-based resin”).

Further, this high molecular weight type silane-modified resin iscontained in the sealing material composition for a skin layer at such aproportion that the polymerized silane amount in the whole resincomponent of the skin layer becomes 300 ppm to 2000 ppm. When anappropriate amount of such a high molecular weight type silane-modifiedpolyethylene-based resin is contained in the sealing materialcomposition for a skin layer, extremely high tensile shear adhesionforce at normal temperature can be imparted to the sealing materialsheet 1. Details of the high molecular type silane-modified resin thatcan be used in the sealing material sheet 1 will be described later.

The density of the sealing material composition for a skin layer is0.880 g/cm³ to 0.910 g/cm³ and more preferably 0.899 g/cm³ or less. Whenthe density of the sealing material composition for a skin layer is setin the above-described range, the adhesion of the sealing material sheet1 can be maintained in a preferable range.

The melting point of the sealing material composition for a skin layermay be 70° C. to 90° C. and is preferably 70° C. to 80° C. As long asthe melting point of the skin layer can be maintained in theabove-described range similarly to the core layer, polyethylene-basedresins each having a different melting point can be appropriately mixedto obtain a sealing material composition for a skin layer. For example,according to a resin composition obtained by mixing three kinds ofpolyethylene-based resins respectively having melting points of 60° C.,90° C., and 97° C. in each amount of 65 parts by mass, 20 parts by mass,and 20 parts by mass, the melting point of the whole skin layer can beset to 73° C., and a blending example of such material resins can beexemplified as a preferable resin blending example of the sealingmaterial composition for a skin layer. When the melting point of thesealing material composition for a skin layer is set to 70° C. orhigher, heat resistance necessary for the sealing material sheet 1 canbe imparted. Further, when the melting point of the sealing materialcomposition for a skin layer is set to 90° C. or lower, the moldingcharacteristics of the sealing material sheet at the time of beingintegrated as the solar-cell module can be maintained in a preferablerange.

The melt mass flow rate (MFR) of the sealing material composition for askin layer may be 3.0 g/10 min or more and less than 5.0 g/10 min, andas long as the MFR is in this range, a polyethylene-based resin havingan MFR of 0.8 g/10 min or more and less than 5.0 g/10 min can beappropriately mixed and used. When the MFR of the sealing materialcomposition for a skin layer is set in the above-described range, theheat resistance and the molding characteristics can be provided to thesealing material sheet 1 at a good balance.

[Silane-Modified Polyethylene-Based Resin]

Regarding the sealing material sheet 1, it is essential that asilane-modified polyethylene-based resin is contained in at least a skinlayer 12, and further, the silane-modified polyethylene-based resincontained in the skin layer 12 is essentially a “high molecular weighttype silane-modified polyethylene-based resin.”

Hereinafter, first, a general “silane-modified polyethylene-based resin”will be described, and then details of the “high molecular weight typesilane-modified polyethylene-based resin” that is an importantconstitution requisite of the invention of the present application willbe described.

The silane-modified polyethylene-based resin is obtained by graftpolymerization of an ethylenically unsaturated silane compound as a sidechain using a linear low-density polyethylene-based resin (LLDPE) or thelike as a main chain. Further, the “silane-modified polyethylene-basedresin” in the present specification is a copolymer obtained bycopolymerization using at least an α-olefin and an ethylenicallyunsaturated silane compound as comonomers and optionally otherunsaturated monomer as a comonomer and includes a product ofmodification or condensation of such a copolymer.

Alternatively, a copolymer of an α-olefin and an ethylenicallyunsaturated silane compound or a product of modification or condensationof the copolymer can be produced, for example, by the following method.First, one or two or more α-olefins and optionally one or two or moreunsaturated monomers are subjected to simultaneous or stepwisepolymerization using a desirable reaction vessel in the presence of aradical polymerization initiator and optionally a chain transfer agentas described above. Then, the polyolefin-based polymer produced by thepolymerization is subjected to graft copolymerization of one or two ormore ethylenically unsaturated silane compounds. Then, further, silanecompound moieties that constitute the graft copolymer produced by thecopolymer are optionally modified or condensed. Through the aboveprocess, a copolymer of the α-olefin and the ethylenically unsaturatedsilane compound or a product of modification or condensation of thecopolymer can be produced.

As the α-olefin, for example, one or more kinds selected from ethylene,propylene, 1-butene, isobutylene, 1-pentene, 2-methyl-1-butene,3-methyl-1-butene, 1-hexene, 1-heptene, 1-octene, 1-nonene, and 1-decenecan be used.

As the ethylenically unsaturated silane compound, for example, one ormore kinds selected from vinyltrimethoxysilane, vinyltriethoxysilane,vinyltripropoxysilane, vinyltriisopropoxysilane, vinyltributoxysilane,vinyltripentyloxysilane, vinyltriphenoxysilane, vinyltribenzyloxysilane,vinyltrimethylenedioxysilane, vinyltriethylenedioxysilane,vinylpropionyloxysilane, vinyltriacetoxysilane, andvinyltricarboxysilane can be used.

As other unsaturated monomers, for example, one or more kinds selectedfrom vinyl acetate, acrylic acid, methacrylic acid, methyl acrylate,methyl methacrylate, ethyl acrylate, and vinyl alcohol can be used.

Examples of the radical polymerization initiator that can be usedinclude organic peroxides such as lauroyl peroxide, dipropionylperoxide, benzoyl peroxide, di-tert-butyl peroxide, t-butylhydroperoxide, and t-butyl peroxybutyrate, molecular oxygen, and azocompound such as azobisisobutyronitrile and azoisobutylvaleronitrile.

Examples of the chain transfer agent that can be used include paraffinichydrocarbons such as methane, ethane, propane, butane, and pentane,α-olefins such as propylene, 1-butene, and 1-hexene, aldehydes such asformaldehyde, acetaldehyde, and n-butyl aldehyde, ketones such asacetone, methyl ethyl ketone, and cyclohexanone, aromatic hydrocarbons,and chlorinated hydrocarbons.

For example, a method for modification or condensation of silanecompound moieties that constitute a random copolymer or a method formodification or condensation of silane compound moieties that constitutea graft copolymer may include a method of carrying out a dehydrationcondensation reaction between silanol groups of silane compound moietiesthat constitute a random copolymer or a graft copolymer with α-olefinand an ethylenically unsaturated silane compound using a silanolcondensation catalyst such as a carboxylate of a metal such as tin,zinc, iron, lead, or cobalt, and an organometallic compound such as atitanate or a chelate compound, an organic base, an inorganic acid, oran organic acid so that a product of modification or condensation of thecopolymer of an α-olefin and an ethylenically unsaturated silanecompound is produced.

As the silane-modified polyethylene-based resin, any of a randomcopolymer, an alternating copolymer, a block copolymer, and a graftcopolymer can be preferably used. However, the silane-modifiedpolyethylene-based resin is more preferably a graft copolymer and evenmore preferably a graft copolymer having a polyethylene main chain forpolymerization and an ethylenically unsaturated silane compound-derivedside chain grafted to the main chain. Such a graft copolymer in whichsilanol groups contributable to adhesion force have a high degree offreedom can improve the adhesion of other member in the solar-cellmodule, particularly, the sealing material sheet to a glass substrate orthe like.

The content of the ethylenically unsaturated silane compound when thesilane-modified polyethylene-based resin is formed is, for example,about 0.001 to 15% by mass, preferably about 0.01 to 5% by mass, andparticularly preferably about 0.05 to 2% by mass with respect to thetotal mass of the copolymer. In a case where the content of theethylenically unsaturated silane compound that constitutes the copolymerof the α-olefin and the ethylenically unsaturated silane compound is inthe above-described range, particularly, adhesion of the sealingmaterial sheet with glass is significantly improved. When the content ofthe silane compound exceeds the above-described range, tensileelongation, heat sealability, and the like of the sealing material sheettend to be degraded, which is not preferable.

In the sealing material sheet 1, of the silane-modifiedpolyethylene-based resins described above, the “high molecular weighttype silane-modified polyethylene-based resin” in a particular molecularweight range is used as a resin essentially added to the sealingmaterial composition for a skin layer.

Regarding the molecular weight of the high molecular weight typesilane-modified polyethylene-based resin used as a resin essentiallyadded to the sealing material composition for a skin layer, the weightaverage molecular weight in terms of polystyrene is 70000 to 120000 andpreferably 90000 to 120000. Incidentally, when the molecular weight ofthe silane-modified polyethylene-based resin exceeds 120000,compatibility with the base resin, which is assumed that the MFR ispreferably about 3.0 g/10 min to 5.0 g/10 min deteriorates, which is notpreferable.

The measurement of the molecular weight of each resin component thatconstitutes the sealing material sheet 1 can be performed using aconventionally known GPC method. Incidentally, since polyolefin ishardly dissolved in a solvent at normal temperature, it is preferablethat the molecular weight is measured using a solvent such astrichlorobenzene or o-dichlorobenzene by GPC of a high temperature of140 to 150° C. Particularly in the case of the sealing material sheet 1,in order to measure the molecular weight of the silane-modifiedpolyethylene-based resin contained in the skin layer 12, the molecularweight of the silane-modified polyethylene-based resin can be specifiedby separating the skin layer of the sealing material sheet 1 that is amulti-layer sheet, combining the molecular weight measurement andcomponent analysis by GPC-FTIR or the like, and reading the molecularweight corresponding to a component identified by IR. Incidentally, anumber average molecular weight Mn, a weight average molecular weightMw, and a degree of dispersion d in a case where a polymer having amolecular weight Mi (g/mol) is Ni (polymers) in the skin layer of thesealing material sheet 1 are defined by the following equations,respectively.

Number average molecular weight Mn=Σ(MiNi)/ΣNi

Weight average molecular weight Mw=Σ(Mi²Ni)/ΣMiNi

Degree of dispersion d=Mw/Mn

[Other Additive Components]

To the respective sealing material compositions for a core layer and askin layer that constitute the sealing material sheet 1, particularly,the sealing material composition for a skin layer, an adhesion improvercan be appropriately added. As the adhesion improver, a known silanecoupling agent can be used, but a silane coupling agent having an epoxygroup (hereinafter, also referred to as an “epoxy-based silane couplingagent”) or a silane coupling agent having a mercapto group (hereinafter,also referred to as a “mercapto-based silane coupling agent”) can beparticularly preferably used.

Other components can be further contained in the respective sealingmaterial compositions for a core layer and a skin layer. For example,components such as a weathering master batch for impartingweatherability to the sealing material sheet, various fillers, a lightstabilizer, an ultraviolet ray absorbent, and a heat stabilizer can beexemplified. The contents of those components vary depending on theshapes, densities, and the like of particles thereof, but are preferablyin a range of about 0.001% by mass to 5% by mass in the respectivesealing material compositions. By including such additives, the stablemechanical strength, effect on preventing yellowing or cracks, and thelike for a long period of time can be imparted to the sealing materialsheet.

<Sealing Material Sheet>

The sealing material sheet of the present invention can be manufacturedby melt molding the aforementioned sealing material composition.

As illustrated in FIG. 1, the sealing material sheet 1 includes the corelayer 11 and the skin layer 12 is formed on both surfaces of the corelayer 11. However, even in the case of a sealing material sheet in whicha core layer has a multi-layer constitution and other functional layersare disposed in the core layer, as long as the sealing material sheethas the core layer and the skin layer that have the constitutionrequisites of the present invention, and other constitution requisitesof the present invention, the sealing material sheet is within the scopeof the present invention.

The MFR of the sealing material sheet 1 having the three-layerconstitution including the core layer 11 and the skin layer 12 is 3.0g/10 min or more and less than 5.0 g/10 min and preferably 3.3 g/10 minor more and less than 3.8 g/10 min in terms of average of the wholelayer. When the MFR of the sealing material sheet 1 is less than 5.0g/10 min, heat resistance necessary for the sealing material sheet 1 canbe provided. Further, when the MFR thereof is 3.0 g/10 min or more,molding characteristics necessary for the sealing material sheet 1 canbe provided.

The total thickness of the sealing material sheet 1 having thethree-layer constitution including the core layer 11 and the skin layer12 is preferably 250 μm to 600 μm and more preferably 300 μm to 550 μm.When the total thickness is less than 250 μm, impact cannot besufficiently alleviated, but when the total thickness is 250 μm or more,for example, even in a case where the total thickness of the sealingmaterial sheet 1 is decreased to about 250 μm, the sealing materialsheet 1 can be formed to have both the molding characteristics and theheat resistance at a sufficiently preferable level. Incidentally, in acase where the total thickness exceeds 600 μm, the effect of furtherimproving the impact alleviation effect is hardly obtainable, it is alsonot possible to respond to the demand for decreasing the thickness ofthe solar-cell module, and this is not economical, which is notpreferable.

Further, the thickness of the core layer 11 in the sealing materialsheet 1 is 200 μm to 400 μm and preferably 250 μm to 350 μm. Further,the thickness of each layer of the skin layer 12 is 30 μm to 100 μm andpreferably 35 μm to 80 μm. Further, the total thickness of the two skinlayers 12 laminated on both surfaces of the core layer is 1/20 to ⅓ andpreferably 1/15 to ¼ of the total thickness of the sealing materialsheet 1. When the thickness of each layer of the sealing material sheet1 is set in such a range, the heat resistance and the moldingcharacteristics of the sealing material sheet 1 can be maintained in afavorable range.

The sealing material sheet 1 is formed by various molding methodsgenerally used for molding a general thermoplastic resin, such asinjection molding, extrusion molding, blow molding, compression molding,and rotational molding. As an example of the method for forming asealing material sheet in a case where the sealing material sheet is amultilayer film, there is a method for forming a sealing material sheetby coextrusion molding using three kinds of melt kneading/extrudingmachines.

However, in any methods described above, the melt molding temperature inmanufacturing of the sealing material sheet 1 is preferably the meltingpoint of the base resin of the sealing material composition for a corelayer contained in the sealing material composition+30° C. or higher.Specifically, the melt molding temperature is preferably set to a hightemperature from 175° C. to 230° C. and more preferably set to a hightemperature in a region from 190° C. to 210° C. Since the sealingmaterial composition used in the sealing material sheet 1 is athermoplastic composition not containing a crosslinking agent, it is notnecessary to consider the control of unfavorable crosslinkingprogression during melt molding. According to this, in manufacturing ofthe sealing material sheet using a polyethylene-based resin as a baseresin, limitation on temperature in a case where a thermosetting sealingmaterial composition essentially needing a crosslinking treatment thathas been general in the related art is used does not need to beconsidered, and the melt molding temperature can be set to a highertemperature region in order to improve productivity. According to this,the sealing material sheet 1 can be manufactured with higherproductivity that that of the thermosetting sealing material sheet inthe related art.

<Solar-Cell Module>

The sealing material sheet 1 can be widely used in various solar-cellmodules that are conventionally known. In general, in the solar-cellmodule, a sealing material is disposed in a mode of being interposedbetween both surfaces of the solar cell element and sealing thesurfaces. On the other hand, the sealing material sheet 1 can also bedisposed as a sealing material on both surfaces of the solar cellelement or only a sealing material on any one of the surfaces can alsobe used in the sealing material sheet 1.

The sealing material sheet can be used in various solar-cell modules asdescribed above, but can be particularly preferably used in adouble-sided glass protecting substrate type solar-cell module having alaminated glass structure or a solar-cell module in which a convexportion having a relatively high height such as a lead wire is formed ona solar cell element, such as a thin film solar-cell module.

[Double-Sided Glass Protecting Substrate Type Solar-Cell Module]

FIG. 2 is a cross-sectional view illustrating an example of a layerconstitution of a double-sided glass protecting substrate typesolar-cell module 10 that can be formed using the sealing material sheet1 of the present invention. The solar-cell module 10 includes atransparent front substrate 2, a sealing material 1A of a lightreceiving surface side, a solar cell element 3, a sealing material 1B ofa non-light receiving surface side, and a rear-surface protectingsubstrate 4 which are laminated in this order from a light receivingsurface side of incident light, and the solar cell element 3 is sealedbetween the sealing material 1A of the light receiving surface side andthe sealing material 1B of the non-light receiving surface side.

In the double-sided glass protecting substrate type solar-cell module10, both the transparent front substrate 2 and the rear-surfaceprotecting substrate 4 are a protecting substrate made of glass. As theprotecting substrate made of glass, various glass plate materials thathave been used as a translucent substrate material constituting thesolar-cell module in the related art can be used without particularlimitations. The solar-cell module 10 may include a member other thanthe above-described members.

Further, the solar cell element 3 is also not particularly limited. Thesolar cell element is not limited to a crystalline silicon solar cellproduced using a monocrystalline silicon substrate or a polycrystallinesilicon substrate, but a thin film solar cell (CIGS) obtained usingamorphous silicon, microcrystalline silicon, a chalcopyrite-basedcompound, or the like can also be preferably used.

As the rear-surface protecting substrate 4, a resin sheet having aphysical property typically required in a protecting layer, which isdisposed on the outermost layer of the solar-cell module, such as watervapor barrier property or weathering resistance, can be used. Further,the rear-surface protecting substrate 4 may be a glass substratesimilarly to the transparent front substrate 2. Since the sealingmaterial sheet 1 has favorable adhesion even in any of a metal andglass, even in a case where the rear-surface protecting substrate 4 is asubstrate made of glass, this rear-surface protecting substrate 4 can bepreferably used.

In the solar-cell module having a general constitution in which therear-surface protecting substrate is formed from a resin film havingweathering resistance, in general, in order to maintain the shape of thelaminate formed from each sheet-shaped member that constitutes thesolar-cell module, a protecting frame made of metal or the likesurrounding a circumference of a side surface of the laminate isprovided. However, in the case of the double-sided glass protectingsubstrate type solar-cell module 10 formed by being interposed betweenprotecting substrates made of glass, a so-called flameless structuresolar-cell module in which such a protecting frame is excluded is alsoprovided for decreasing the weight in many cases.

In the double-sided glass protecting substrate type solar-cell module 10having a flameless structure, a high tensile shear adhesion force (anadhesion force according to JIS K 6850 Adhesives-Determination oftensile lap-shear strength of rigid-to-rigid bonded assemblies) atnormal temperature is required in the sealing material. Since thesealing material sheet 1 of the present invention is regarded as asealing material sheet having a particular tensile shear adhesionstrength by specifying the molecular weight of the adhesion resincontained in the skin layer in a high range, the sealing material sheet1 can be particularly preferably used in the double-sided glassprotecting substrate type solar-cell module 10 having a flamelessstructure.

[Thin Film Solar-Cell Module]

FIG. 3 is a cross-sectional view illustrating an example of a layerconstitution of a thin film solar-cell module 10A that can be formedusing the sealing material sheet 1 of the present invention. Thesolar-cell module 10A includes a transparent front substrate 2, a thinfilm solar cell element 3 disposed on a surface of the transparent frontsubstrate 2, a sealing material (the sealing material sheet 1), and arear-surface protecting substrate 4 which are laminated in this orderfrom a light receiving surface side of incident light. In the thin filmsolar-cell module 10A, the sealing material (the sealing material sheet1) is laminated at a non-light receiving surface side of the solar cellelement 3.

Herein, in the solar-cell module 10A, as illustrated in FIG. 4, thereare irregularities due to a metal electrode 31 or a lead wire 32 forpower collection on the surface at the non-light receiving surface sideof the solar cell element 3. In the case of using a sealing materialsheet that uses a polyethylene-based resin as a base resin in therelated art, when heat resistance is intended to be secured byperforming the crosslinking treatment or simply increasing a density, aproblem arises in that voids V due to insufficiency of moldingcharacteristics are formed (see FIG. 5).

However, in a case where the sealing material sheet 1 in which both theheat resistance and the molding characteristics are achieved at a highlevel is disposed on the irregularity surface, the sealing materialsheet 1 also sufficiently wraps around the irregularities due to themetal electrode 31 or the lead wire 32 for power collection which arepresent on the surface of the non-light receiving surface side of thesolar cell element 3 and can prevent the formation of the voids V (seeFIG. 4). That is, in a case where there are irregularities formed byconvex portions of the lead wire 32 or the like on the surface of thesolar cell element like the solar-cell module 10A, the sealing materialsheet 1 can be particularly preferably used. In a case where thethickness of the convex portions of the irregularities is 50% to 90% ofthe thickness of the sealing material sheet 1, the moldingcharacteristics of the sealing material sheet are particularlyexhibited. According to this, as described above, it is possible tosufficiently prevent the formation of the voids V due to existence ofthe irregularities on the surface of the solar cell element.

More specifically, in a case where the lead wire 32 is a lead wirehaving a thickness that is equal to or more than about a thickness (d₁)of 250 μm, the sealing material sheet 1 exhibits a particular effectthat is significantly different from a conventional product. Forexample, as illustrated in FIG. 5, when the sealing material sheet 1formed from a conventionally general polyethylene resin is disposed onthe irregularity surface in a case where the thick lead wire 32 isdisposed, in general, in a case where the thickness (d₁) of the leadwire 32 with respect to a thickness (d₂) of the sealing material sheet 1exceeds 50% as a rough standard, the formation of the voids V describedabove becomes problematic in many cases. However, as illustrated in FIG.4, in a case where the sealing material sheet 1 is disposed on such airregularity surface, when the thickness (di) of the lead wire 32 withrespect to the thickness (d₂) of the sealing material sheet 1 is 90% orless, it is possible to sufficiently prevent the formation of the voidsV described above. Incidentally, in the present invention, in a casewhere a plurality of lead wires are laminated, for example, a case wherelead wires are alternately disposed, the total thickness of theplurality of lead wires in a part at which the plurality of lead wiresare laminated is considered as “the thickness of the lead wire” asdescribed above, that is, “the thickness of the convex portion.”

[Method for Manufacturing Solar-Cell Module]

The solar-cell module 10 can be manufactured by sequentially laminatingthe solar-cell module members constituted of the transparent frontsubstrate 2, the sealing material 1A of the light receiving surfaceside, the solar cell element 3, the sealing material 1B of the non-lightreceiving surface side, the rear-surface protecting substrate 4, and thelike, integrating the laminated members by a vacuum aspiration or thelike, and then, thermocompression-molding the above members in onemolding body by a molding method such as a laminating method.

Examples

Hereinafter, the present invention will be described in more detail withreference to Examples, but the present invention is not limited to thefollowing Examples.

<Manufacturing of Sealing Material Sheet for Solar-Cell Module>

Sealing material composition raw materials described below were mixed ata ratio (parts by mass) in the following Table 1 to obtain sealingmaterial compositions for a core layer and a sealing materialcomposition for a skin layer of sealing material sheets of Examples andComparative Examples. Each resin sheet for making respective sealingmaterial compositions for a core layer and a skin layer was producedusing a ϕ 30 mm extruder and a film molding machine having a T diehaving a width of 200 mm at an extrusion temperature of 210° C. and apulling speed of 1.1 m/min. Further, these respective resin sheets werelaminated to manufacture a sealing material sheet having a three-layerconstitution of each of Examples and Comparative Examples that includesa core layer and a skin layer disposed on both outermost surfaces. Thethicknesses of the respective sealing material sheets of Examples andComparative Examples were all set to a total thickness of 450 μm.Regarding the thickness ratio of each layer of the sealing materialsheet having a three-layer constitution of each of Examples andComparative Examples, in all of the sealing material sheets, thethickness ratio of the skin layer:the core layer:the skin layer was setto 1:8:1 (the total thickness of the skin layers (total of two layers)being ¼ of the total thickness of the sealing material sheet).Incidentally, regarding Comparative Example 5, a single-layer sealingmaterial sheet having a thickness of 450 μm was formed.

As a material resin of the sealing material composition for molding eachresin sheet for a sealing material sheet, the following respective rawmaterials were used. Polyethylene-based resins 1 to 5 (respectivelydescribed as “PE1 to PE5” in Table): all being metallocene-based linearlow-density polyethylene-based resin (M-LLDPE). The density, the meltingpoint, and the MFR at 190° C. were respectively as described in Table 1.Silane-modified polyethylene-based resin 1 (described as “PS1” inTable):

a silane-modified polyethylene-based resin obtained by mixing 2 parts bymass of vinyltrimethoxysilane and 0.15 part by mass of dicumyl peroxideas a radical generating agent (reaction catalyst) with respect to 100parts by mass of metallocene-based linear low-density polyethylene-basedresin having a density of 0.900 g/cm³ and an MFR of 2.0 g/10 min andmelting and kneading the mixture at 200° C. Density of 0.900 g/cm³, MFRof 1.0 g/10 min. Melting point of 90° C. Silane-modifiedpolyethylene-based resin 2 (described as “PS2” in Table):a silane-modified polyethylene-based resin obtained by mixing 2 parts bymass of vinyltrimethoxysilane and 0.15 part by mass of dicumyl peroxideas a radical generating agent (reaction catalyst) with respect to 100parts by mass of metallocene-based linear low-density polyethylene-basedresin having a density of 0.880 g/cm³ and an MFR of 3.5 g/10 min andmelting and kneading the mixture at 200° C. Density of 0.880 g/cm³, MFRof 2.0 g/10 min. Melting point of 60° C. Silane-modifiedpolyethylene-based resin 3 (described as “PS3” in Table):a silane-modified polyethylene-based resin obtained by mixing 2 parts bymass of vinyltrimethoxysilane and 0.15 part by mass of dicumyl peroxideas a radical generating agent (reaction catalyst) with respect to 100parts by mass of metallocene-based linear low-density polyethylene-basedresin having a density of 0.880 g/cm³ and an MFR of 30.0 g/10 min andmelting and kneading the mixture at 200° C. Density of 0.885 g/cm³, MFRof 13.0 g/10 min. Melting point of 58° C.:2 parts by mass of vinyltrimethoxysilane and 0.15 part by mass ofdicumyl peroxide as a radical generating agent (reaction catalyst) withrespect to 100 parts by mass of the base resin were mixed and melted andkneaded at 200° C. to obtain a silane-modified polyethylene-based resinhaving a density of 0.885 g/cm³ and an MFR of 13 g/10 min. Melting pointof 58° C.

<Weight Average Molecular Weight of Skin Layer>

The weight average molecular weight of the silane-modifiedpolyethylene-based resin contained in each skin layer of Examples 1 and2 and Comparative Example 1 was measured by a measurement method usingthe aforementioned GPC method. The results are presented in Table 2.

TABLE 1 Polyethylene Silane-modified polyethylene PE1 PE2 PE3 PE4 PE5PS1 PS2 PS3 Density 0.880 0.898 0.898 0.905 0.919 0.900 0.880 0.885(g/cm³) MFR 3.5 3.5 3.5 3.5 3.5 1.0 2.0 13.0 (g/10 min.) Melting point60 90 90 97 105 90 60 58 (° C.) Example1 Core layer 65 5 — 32 — 3 — —Skirt layer 65 5 — 20 — 15 — — Example2 Core layer 65 5 32 — — — 3 —Skirt layer 65 5 20 — — — 15 — Example3 Core layer — 5 — — 97 3 — —Skirt layer — 5 85 — — 15 — — Comparative Example1 Core layer 65 5 — 32— — — 3 Skirt layer 65 5 — 20 — — — 15 Comparative Example2 Core layer —5 — — 97 3 — — Skirt layer — 5 — 85 — 15 — — Comparative Example3 Corelayer 97 5 — — — 3 — — Skirt layer 65 5 — 20 — 15 — — ComparativeExample4 Single layer — 60 — — — — — 40

TABLE 2 Weight average molecular weight Example1 91000 Example2 76000Comparative Example1 48000

Evaluation Example 1: Molding Characteristics

A lead wire (diameter: 250 μm) was disposed on the surface of colorlessstrengthened glass having a flat surface, the lead wire was furthercovered, and a laminate obtained by laminating each sealing materialsheet of Examples and Comparative Examples cut into a size of 150 mm×150mm was subjected to a vacuum heating lamination treatment at a settemperature of 150° C. under a vacuum aspiration for 3 minutes and anatmospheric pressurization of 7 minutes, thereby obtaining a sample forsolar-cell module evaluation of each of Examples and ComparativeExamples. The resin temperature (achieving temperature) of the sealingmaterial sheet in lamination during the heating treatment was 147° C.These samples for solar-cell module evaluation were visually observed,and molding characteristics were evaluated by the following evaluationcriteria.

(Evaluation Criteria)

A: The sealing material sheet completely followed irregularities of thefacing base material surface. Formation of voids was not observed.B: Five or less of air bubbles within 2 mm² were observed.C: A part of the sealing material sheet did not completely followirregularities of the facing base material surface and lamination defectparts (voids) were partially formed in the vicinity of the lead wire.The evaluation results are described as “Molding characteristics” inTable 3.

Evaluation Example 2: Heat Resistance Test

A heat-resistant creep test was performed as a heat resistance test. Onesheet of the sealing material sheet of each of Examples and ComparativeExamples cut into a size of 5 cm×7.5 cm was superimposed on the sameglass plate as in Evaluation Example 1 described above, the same glassplate as in Evaluation Example 1 having a size of 5 cm×7.5 cm wassuperimposed from the above, a vacuum heating lamination treatment wasperformed under the same conditions as in Evaluation Example 1 toprepare samples for evaluation. Thereafter, large-sized glass was placedvertically and left at 90° C. for 12 hours, the moving distance (mm) ofthe glass plate having a size of 5 cm×7.5 cm after being left wasmeasured, and the heat resistance was evaluated by the followingevaluation criteria.

(Evaluation Criteria)

A: 0.0 mm

B: more than 0.0 mm and less than 1.0 mmC: 1.0 mm or moreThe evaluation results are described as “Heat resistance” in Table 3.

Evaluation Example 3: Tensile Shear Adhesion Strength

The tensile shear adhesion strength as an index of adaptivity to thedouble-sided glass protecting substrate type module was measured. Themeasurement was performed by the test method according to JIS K 7197.Two sheets of the same glass plate as in Evaluation Example 1 describedabove were used, the sealing material sheets of Examples and ComparativeExamples cut into a size of 2.5 cm×1.27 cm were placed between the twosheets of the glass plate and were adhered by performing a vacuumheating lamination treatment under the same conditions as in EvaluationExample 1 to prepare samples for evaluation. Thereafter, the tensileshear adhesion strength at a tensile rate of 1.27 mm/min was measured bythe above-described test method, and the tensile shear adhesion strengthwas evaluated by the following evaluation criteria.

(Evaluation Criteria)

A: 1000 N or moreB: 500 N or more and less than 1000 NC: less than 500 NThe evaluation results are described as “Tensile shear adhesionstrength” in Table 3.

TABLE 3 Core layer Skin layer Average of whole layer Melting MeltingMelting Density MFR point Density MFR point Density MFR point (g/cm³)(g/10 min.) (° C.) (g/cm³) (g/10 min.) (° C.) (g/cm³) (g/10 min.) (° C.)Example1 0.889 3.4 74 0.888 3.1 73 0.889 3.4 73 Example2 0.888 3.5 730.886 3.3 68 0.888 3.4 72 Example3 0.917 3.4 104 0.898 3.1 90 0.912 3.4100 Comparative Example 1 0.888 3.8 73 0.886 4.9 68 0.888 4.1 72Comparative Example2 0.917 3.4 104 0.904 3.1 96 0.914 3.4 102Comparative Example3 0.881 3.6 62 0.888 3.1 73 0.883 3.4 62 ComparativeExample4 — — — — — — 0.891 7.3 78

TABLE 4 Tensile shear Molding adhesion strength charac- Heat Eval-tristics resistance Strength(N) uation Example1 A A 1200 A Example2 A B1000 A Example3 B A 2300 A Comparative Example1 A B 450 C ComparativeExample2 C A 2000 A Comparative Example3 A C 1000 A Comparative Example4A A 450 C

From Tables 1 to 4, it is found that the sealing material sheet of thepresent invention is a sealing material sheet using a polyethylene-basedresin and is a sealing material sheet for a solar-cell module that hashigh productivity without performing crosslinking processing, and has ahigh tensile shear adhesion force at normal temperature at a high levelin addition to heat resistance and molding characteristics.

1. A sealing material sheet for a solar-cell module, the sealingmaterial sheet being a multi-layer sheet using a polyethylene-basedresin as a base resin and including a core layer and a skin layerdisposed on both outermost surfaces, wherein the core layer has adensity of 0.880 g/cm³ to 0.930 g/cm³ and a melting point of 70° C. orhigher, the skin layer has a density of 0.880 g/cm³ to 0.900 g/cm³ and amelting point of 90° C. or lower, and the skin layer contains asilane-modified polyethylene-based resin, a weight average molecularweight of the silane-modified polyethylene-based resin contained in theskin layer in terms of polystyrene being 70000 to 120000, a polymerizedsilane amount of the skin layer in the whole resin component being 300ppm to 2000 ppm.
 2. The sealing material sheet according to claim 1,wherein the weight average molecular weight of the silane-modifiedpolyethylene-based resin contained in the skin layer in terms ofpolystyrene is 90000 to
 120000. 3. The sealing material sheet accordingto claim 1, wherein melting points of the core layer and the skin layerare both 70° C. to 80° C.
 4. A solar-cell module obtained bysequentially laminating a transparent front substrate, a sealingmaterial of a light receiving surface side, a solar cell element, asealing material of a non-light receiving surface side, and arear-surface protecting substrate, the sealing material of the lightreceiving surface side and the sealing material of the non-lightreceiving surface side being the sealing material sheet according toclaim
 1. 5. The solar-cell module according to claim 4, wherein both thetransparent front substrate and the rear-surface protecting substrateare a protecting substrate made of glass.
 6. The solar-cell moduleaccording to claim 5, wherein the solar-cell module is a framelessmodule having no protecting frame that surrounds a circumference of aside surface of a module laminate interposed between the protectingsubstrates made of glass to maintain a shape of the module laminate. 7.The solar-cell module according to claim 4, wherein, in a surface of thesolar cell element, convex portions formed by a part of the surfaceprotruding in a line-shaped manner or a dot-shaped manner exist, theconvex portions being buried inside the sealing material sheet laminatedon the surface, and a thickness of the convex portion is 50% to 90% of athickness of the sealing material sheet laminated on the surface of thesolar cell element.